Ammoxidation process

ABSTRACT

Olefins, such as propylene are oxidized to form acrolein or ammoxidized to form acrylonitrile in the presence of a catalyst containing the elements antimony, uranium, iron and tungsten in a catalytic active oxidized state.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a division of application Ser. No. 320,372 filed Jan. 2, 1973, now U.S. Pat. No. 3,886,096 issued May 27, 1975.

BACKGROUND OF THE INVENTION

This invention relates to an improved oxidation and/or ammoxidation catalyst system containing the elements antimony, uranium, iron and tungsten and to a method for preparing such catalyst system.

It is well known that olefins can be oxidized to oxygenated hydrocarbons such as unsaturated aldehydes and acids, for example, acrolein and methacrolein, acrylic and methacrylic acid. It is also well known that olefins can be ammoxidized to unsaturated nitriles such as acrylonitrile and methacrylonitrile. The value of such oxygenated hydrocarbons and unsaturated nitriles is generally well recognized with acrylonitrile being among the most valuable monomers available to the polymer industry for producing useful polymeric products.

Various catalytic processes are known for the oxidation and/or ammoxidation of olefins. Such processes commonly react an olefin or an olefin-ammonia mixture with oxygen in the vapor phase in the presence of a catalyst. For the production of acrolein and acrylonitrile, propylene is the generally used olefin reactant and for the production of methacrolein and methacrylonitrile, isobutylene is the generally used olefin reactant.

A catalyst system composed of the oxides of antimony and uranium and the oxidation and ammoxidation of olefins using such catalyst has been described in U.S. Pat. Nos. 3,198,750 and 3,308,151. These patents describe preparation of the catalyst by precipitation wherein the oxides of the elements are contained in a slurry which is filtered to remove soluble salts and recover the catalytic components as the filter cake.

In the catalytic oxidation and/or ammoxidation of olefins, the commercial utility of a catalyst system is highly dependent upon the cost of the system, the conversion of the olefin and the yield of the desired product. In many cases a reduction in the cost of a catalyst system in the order of a few pennies per pound or a 1% increase in the yield of a desired product represents a tremendous commercial economical savings. Accordingly, research efforts are continuously being made to define new or improved catalyst systems and methods of making new and old catalyst systems to reduce the cost and/or to upgrade the activity and selectivity of such catalyst systems in particular processes.

SUMMARY

This invention is directed to an improved catalyst system containing the elements antimony, uranium, iron and tungsten having commercial activity and selectivity for the catalytic oxidation and/or ammoxidation of olefins and to an improved method of making such catalyst system.

Accordingly, typical objects of this invention are to provide: (1) an improved oxidation and/or ammoxidation catalyst system containing oxygen, antimony, uranium, iron and tungsten, (2) an improved process for the preparation of a catalyst system containing oxygen, antimony, uranium, iron and tungsten, and (3) an improved olefin conversion process.

Other objects, aspects and advantages of this invention will become apparent to those skilled in the art upon further study of this disclosure and the appended claims.

In accordance with this invention, a new oxidation/ammoxidation catalyst system based on the elements antimony, uranium, iron and tungsten is provided. The elements are in combination with oxygen and may exist as individual oxides or as complexes of two or more of the elements and oxygen or as a combination of oxides and complexes. The atomic ratio of the elements present in the catalyst system may vary over a wide range. Generally speaking the catalyst may be defined by the following empirical formula:

    Sb.sub.a U.sub.b Fe.sub.c W.sub.d O.sub.e

wherein a is 1-10, b is 0.01 to 1, c is 0.01 to 1, d is 0.001 to 0.1 and e is a number taken to satisfy the average valences of the Sb, U, Fe and W in the oxidation states in which they exist in the catalyst.

The catalyst can be prepared starting with individual oxides or sulfates of the elements. A preferred method of preparing the catalyst is to combine the oxides or sulfates of the elements with sulfuric acid. When antimony sulfate is used as a starting material, it can be added to water wherein sulfuric acid is obtained. Nitric acid is used to oxidize the sulfate salts of the elements or to further oxidize the oxides of the elements. After the acid mixture has digested, the pH of the mixture is adjusted to about 8 followed by filtration.

After filtering the mixture, the filter cake can be dried at a temperature of from about 100°C to about 180°C. A suitable drying temperature is about 110°C. However, the drying can be obtained at higher temperatures such as up to about 650°C. The time required for drying the filter cake can range from an hour up to about 64 hours. Obviously, the drying temperature selected will dictate the required drying time with the lower temperature requiring the longer time. Also, the filter cake may be dried at different temperatures, for example at 110°C for from 2 to 64 hours and then at a temperature of from about 250°C to about 650°C for from 2 to 24 hours.

After the filter cake is dried, it is further heated at an elevated temperature to obtain the active catalytic form of the elements. This calcination of the catalyst is conducted at a temperature in the range of from about 500°C to about 1150°C. The time for calcination can vary and depends upon the temperatures employed. Generally, a time period of 2 to 24 hours at the designated temperatures is sufficient. The calcination may be conducted in the presence of oxygen (air); however, the catalyst may also be made active by calcining it in the absence of oxygen, such as in a nitrogen atmosphere.

The catalyst can be employed without support, and will display excellent activity. It also can be combined with a support, and preferably at least 5% up to about 90% preferably 5 to 50%, of the supporting compound by weight of the entire composition is employed in this event. Any known support materials can be used, such, for example, silica, alumina, zirconia, alundum, silicon carbide, alumina-silica, and the inorganic phosphates, silicates, aluminates, borates and carbonates stable under the reaction conditions to be encountered in the use of the catalyst.

The improved catalyst of this invention exhibits exceptional utility in the conversion of olefins with or without the presence of ammonia. The olefins employed as reactants for conversion by the catalyst of this invention may be open chain as well as cyclic and include, for example, propylene, butene-1, butene-2, isobutene, pentene-1, pentene-2, 3-methyl butene-1, 2-methyl butene-2, hexene-1, hexene-2, 4-methyl pentene-1, 3,3 dimethyl butene-1, 4-methyl pentene-2, octene-1, cyclopentene, cyclohexene, and the like. Particularly, when the catalyst of this invention is used as merely an oxidation catalyst, it is particularly adapted to the conversion of propylene to acrolein and isobutylene to methacrolein. Of course, mixtures of olefins may be employed and mixtures of olefins with other hydrocarbons are applicable to the process of this invention. When the catalyst of this invention is to be used as an ammoxidation catalyst, the olefins as aforestated are applicable. However, the catalyst of this invention is particularly adapted to the conversion of propylene with ammonia and oxygen to acrylonitrile at 250°C to 650°C.

The molar ratio of oxygen to the olefin in the feed will generally be in the range of 0.5:1 to 4:1 with a preferred ratio being 1:1 to 3:1. The molar ratio of ammonia to olefin in the feed will generally be in the range of 0.5:1 to 5:1 and preferably slightly over the stoichiometric ratio of 1:1 ammonia:olefin will be employed.

While ammonia is most generally employed as the nitrogen providing compound, other nitrogen containing materials may be employed which decompose to produce reactive nitrogen under the reaction conditions. Any source of oxygen, pure or in admixture with inerts, may be employed in the process of this invention. Air is a satisfactory source of oxygen for use in this invention.

The catalyst system of this invention can be advantageously employed for synthesizing styrene from ethylbenzene and oxygen, butadiene from butenes and oxygen, acrolein or methacrolein from propylene or isobutylene and oxygen, acrylonitrile or methacrylonitrile from propylene or isobutylene, ammonia and oxygen, isoprene from 2-methyl butene-2 and oxygen, and 2-cyano-1,3-butadiene from 2-methyl butene 2 or isoprene, ammonia and oxygen.

DESCRIPTION OF PREFERRED EMBODIMENTS

The following Examples are presented as illustrative of the invention and, as such, are not intended to be restrictive upon the specific materials, quantities and operation variables specifically set forth therein.

As used in the examples, the following terms have the following definitions: ##EQU1##

The apparatus employed in carrying out the runs in this example is a fluidized bed type reactor. The reactor consists of a 14 mm. inside diameter 96% quartz glass tube fitted at the bottom with a fritted disc for supporting a catalyst bed of up to 50 ml. in volume and fitted at the top with another fritted disc to remove entrained catalyst from the reactor effluent. A thermowell of 4 mm. outside diameter 96% quartz glass extends through the center of the catalyst bed to the fritted disc. The reactor tube is jacketed with a larger tube in which sand is fluidized for providing even heat distribution. The entire reactor assembly is placed in a controlled, hinged tube furnace. The reactant gases are premixed and heated to about 470°C before entering the bottom of the reactor through a single inlet tube. The effluent gases from the reactor are heated to prevent condensation prior to chromatographic analysis.

EXAMPLE I

Five catalyst systems composed of antimony, uranium, iron and tungsten are prepared by adding antimony and uranium oxides and iron sulfate to a sulfuric acid solution containing 83 grams of 98% H₂ SO₄ and 200 ml. of water at about 80°C. The mixture is stirred for about 3 hours. Nitric acid is added to the mixture which is then heated for one to two hours to further oxidize the elements. After cooling the mixture the pH is adjusted to about 8 with ammonium hydroxide. The mixture is allowed to digest about 16 hours. After digestion the mixture is filtered and the precipitate is washed with water. The precipitate is mixed with silica sol (Ludox AS) and either ammonium tungstate or phosphotungstic acid. This mixture is evaporated to dryness and further dried at about 110°C for about 16 hours. The resulting catalyst is calcined at 900°C for 16 hours. The quantities of the various components used in making catalyst systems are given in the following Table I.

                                      TABLE I                                      __________________________________________________________________________     COMPONENT                                                                               CAT.A                                                                               CAT.B                                                                               CAT.C                                                                               CAT.D  CAT.E                                           __________________________________________________________________________     Sb.sub.2 O.sub.3 (grams)                                                                56.5 56.5 56.5 54.7   54.7                                            U.sub.3 O.sub.8 (grams)                                                                 18.25                                                                               18.25                                                                                --  14.0   14.0                                            FeSO.sub.4.7H.sub.2 O                                                           (grams) 18.12                                                                               18.12                                                                               36.24                                                                               27.8   27.8                                            (NH.sub.4).sub.6 W.sub.7 O.sub.24.                                              6H.sub.2 O(grams)                                                                       0.7  --   --   --     --                                             P.sub.2 O.sub.5.24WO.sub.3.                                                     51H.sub.2 O(grams)                                                                      --   1.43                                                                                .72  .83    .83                                            Silica sol                                                                      (Ludox AS)                                                                     (grams) 58.7 58.7 58.7 58.7   93.0                                            ATOMIC RATIO                                                                   Sb/U/Fe/W                                                                               3:0.5-                                                                              3:0.5:                                                                              3:0:1:                                                                              2.5:0.33:                                                                             2.5:0.33:                                                0.5: 0.5: 0.02 0.66:  0.66:                                                    0.02 0.04      0.02   0.02                                            SiO.sub.2 %                                                                             17   17   19.5 17.5   25                                              __________________________________________________________________________

EXAMPLE II

Four catalyst systems made according to the general procedure of Example I are used in the conversion of propylene and ammonia to acrylonitrile using the apparatus previously described. The feed composition in these comparative runs is 8.5% ammonia, 7.4% propylene, 17.7% oxygen and 66.4% helium. In each run the temperature is about 470 °C and the pressure is atmospheric. Other process data and the results are given in Table II. The catalysts are identified as:

A -- sb₃ U₁ W₀.02

B -- sb₃ Fe₁ W₀.02

C -- sb₃ U₀.5 Fe₀.5

D -- sb₃ U₀.5 Fe₀.5 W₀.02

                                      TABLE II                                     __________________________________________________________________________     Catalyst   A       B       C       D                                           __________________________________________________________________________     Catalyst Weight                                                                 (grams)   30  30  40  40  25  25  30  30                                      Contact Time*                                                                   (gm.sec./ml.)                                                                  at STP    6   6   8   8   5   5   6   6                                       Percent Propylene                                                               Converted 94.2                                                                               95.1                                                                               98.0                                                                               97.7                                                                               99.7                                                                               96.5                                                                               95.3                                                                               96.4                                    Percent Propylene                                                               to Acrylonitrile                                                                         59.9                                                                               63.9                                                                               66.7                                                                               64.8                                                                               68.3                                                                               78.8                                                                               78.5                                                                               79.9                                    __________________________________________________________________________                   Weight of Catalyst (grams)                                       *Contact time determined as                                                                               at STP                                                            Feed Flow rate (ml./sec.)                                   

The above example shows the improved ammoxidation activity of the four component catalyst system of this invention compared with three component catalysts.

EXAMPLE III

Three catalyst systems made according to the general procedure of Example I are used in the conversion of propylene and ammonia to acrylonitrile using the apparatus previously described. The feed composition in these comparative runs is 8.9% ammonia, 8.5% propylene, 17.4% oxygen and 65.2% helium. In each run the temperature is about 470°C, the pressure is atmospheric, 30.0 grams of catalyst is used and the contact time is 6 gm.sec./ml (at STP). Other process data and the results are given in Table III. The catalysts are identified as:

A -- sb₂.5 U₀.33 Fe₀.66 W₀.04

B -- sb₃ U₀.33 Fe₀.66 W₀.04

C -- sb₃.5 U₀.33 Fe₀.66 W₀.04

                  TABLE III                                                        ______________________________________                                         Catalyst    A          B          C                                            Percent Propylene                                                              Converted   92.8    95.2   91.9  91.4 88.3  89.8                               Percent Propylene                                                              to Acrylonitrile                                                                           74.6    76.6   75.6  73.6 70.5  71.4                               ______________________________________                                                         Weight of Catalyst (grams)                                     *Contact time determined as      at STP                                                        Feed Flow Rate (ml./sec.)                                 

The above example shows that various atomic ratios of antimony in the catalyst system of this invention are useful.

EXAMPLE IV

Three catalyst systems made according to the general procedure of Example I are used in the conversion of propylene and ammonia to acrylonitrile using the apparatus previously described. The feed composition in these comparative runs is 8.5% ammonia, 7.4% propylene, 17.7% oxygen and 66.4% helium. In each run the temperature is about 470°C and the pressure is atmospheric. Other process data and the results are given in Table IV. The catalysts are identified as:

A -- sb₂.5 U₀.5 Fe₀.5 W₀.02 -- 17.5% SiO₂

B -- sb₂.5 U₀.33 Fe₀.66 W₀.02 ≠-- 17.5% SiO₂

C -- sb₂.5 U₀.2 Fe₀.8 W₀.06 -- 25.6% SiO₂

                  TABLE IV                                                         ______________________________________                                         Catalyst    A          B          C                                            Catalyst Weight                                                                (grams)     25      25     25    25   25    25                                 Contact Time*                                                                  (gm.sec./ml.)                                                                               5       5      5     5    7     7                                 at STP                                                                         Percent Propylene                                                              Converted   92.7    91.5   93.6  92.9 88.6  87.1                               Percent Propylene                                                              to Acrylonitrile                                                                           79.5    77.8   77.3  76.5 65.8  64.8                               ______________________________________                                                         Weight of Catalyst (grams)                                     *Contact time determined as      at STP                                                        Feed Flow Rate (ml./sec.)                                 

The above example shows that various atomic ratios of uranium and iron in the catalyst system of this invention are useful.

EXAMPLE V

Two catalyst systems made according to the general procedure of Example I are used in the conversion of propylene and ammonia to acrylonitrile using the apparatus previously described. The feed composition in these comparative runs is 8.9% ammonia, 8.5% propylene, 17.5% oxygen and 65.1% helium. In each run the temperature is about 490°C and the pressure is atmospheric. Other process data and the results are given in Table V. The catalysts are identified as:

A -- sb₃ U₀.33 Fe₀.66 W₀.04 -- 25% SiO₂

B -- sb₃ U₀.33 Fe₀.66 W₀.04 -- 50% SiO₂

                  TABLE V                                                          ______________________________________                                         Catalyst     A             B                                                   Catalyst Weight                                                                (grams)      30       30       30     30                                       Contact Time*                                                                  (gm.sec./ml.)                                                                  at STP        6        6        6      6                                       Percent Propylene                                                              Converted    94.0     93.7     91.9   91.4                                     Percent Propylene                                                              to Acrylonitrile                                                                            76.5     75.9     75.6   73.6                                     ______________________________________                                                         Weight of Catalyst (grams)                                     *Contact time determined as      at STP                                                        Feed Flow rate (ml./sec.)                                 

This example shows that various percentages of support material in the catalyst system of this invention are useful.

EXAMPLE VI

Four catalyst systems prepared according to the general procedure of Example I are used in the conversion of propylene and ammonia to acrylonitrile using the apparatus previously described. The feed composition in these comparative runs in 8.9% ammonia, 8.5% propylene, 17.4% oxygen and 55.2% helium. In each run the temperature is about 470°C and the pressure is atmospheric. Other process data and the results are given in Table VI. The catalysts are identified as:

A -- sb₂.5 U₀.33 Fe₀.66 W₀.04 -- 25% SiO₂

B -- sb₂.5 U₀.33 Fe₀.66 W₀.05 -- 25% SiO₂

C -- sb₂.5 U₀.33 Fe₀.66 W₀.06 -- 25% SiO₂

D -- sb₂.5 U₀.33 Fe₀.66 W₀.07 -- 30% SiO₂

                                      TABLE VI                                     __________________________________________________________________________     Catalyst  A       B       C       D                                            Catalyst Weight                                                                (grams)   30  30  30  30  30  30  30  30                                       Contact Time*                                                                  (gm.sec./ml.)                                                                  at STP     6   6   6   6   6   6   6   6                                       Percent Propylene                                                              Converted 92.8                                                                               95.2                                                                               95.6                                                                               91.8                                                                               92.5                                                                               88.5                                                                               94.8                                                                               91.0                                     Percent Propylene                                                              to Acrylonitrile                                                                         74.6                                                                               76.6                                                                               78.3                                                                               64.4                                                                               75.2                                                                               71.3                                                                               74.9                                                                               70.9                                     __________________________________________________________________________                      Weight of Catalyst (grams)                                    *Contact time determined as   at STP                                                            Feed Flow Rate (ml./sec.)                                

The above example shows that various atomic ratios of the tungsten in the catalyst system of this invention are useful.

EXAMPLE VII

The catalyst system systems of Example I are used in the conversion of isobutylene to methacrylonitrile using the apparatus previously described. Methacrylonitrile is obtained using each catalyst with a feed composition of 8.9% ammonia, 8.5% isobutylene, 17.5% oxygen and 65.1% helium, all on a volume basis, at a temperature of 500°C and atmospheric pressure.

EXAMPLE VIII

The antimony-uranium-iron-tungsten catalysts of Example I are used in the conversion of propylene to acrolein using the apparatus previously described. Acrolein is obtained using each catalyst with a feed composition of 7.0% propylene, 11.0% oxygen and 82% helium, all on a volume basis, at a temperature of 500°C and atmospheric pressure.

It will be obvious to persons skilled in the art that various modifications may be made in the improved catalyst and process as described in this application. Accordingly, it is intended that all such modifications which reasonably fall within the scope of the appended claims are a part hereof. 

What is claimed is:
 1. A process for producing acrylonitrile or methacrylonitrile which comprises reacting an olefin selected from the group consisting of propylene and isobutylene with ammonia and oxygen in amounts such that the molar ratio of ammonia to olefin is in the range from about 0.5:1 to 5:1 and the molar ratio of oxygen to olefin is from about 0.5:1 to 4:1 at a temperature in the range from about 250° to 650°C in contact with a catalyst system consisting essentially of the elements antimony, uranium, iron and tungsten in a catalytic active oxidized state represented by the formula

    Sb.sub.a U.sub.b Fe.sub.c W.sub.d O.sub.e

wherein a is 1-10, b is 0.01-1, c is 0.01-1, d is 0.001-0.1 and e is a number taken to satisfy the average valences of the Sb, U, Fe and W in their catalytic active oxidation states prepared by forming a mixture of oxides or sulfates of antimony, uranium and iron in sulfuric acid, oxidizing said mixtures with nitric acid, digesting the resulting mixture, adjusting the pH to about 8, filtering the mixture, mixing the filter cake with ammonium tungstate or phosphotungstic acid, evaporating the filter cake mixture to dryness, then heating the dried filter cake mixture at a temperature from about 500° to about 1150°C to form said catalytic active oxidation states.
 2. The process of claim 1 wherein said catalyst system is carried on a support.
 3. The process of claim 2 wherein said mixture is formed from Sb₂ O₃, U₃ O₈, and FeSO₄ .7H₂ O.
 4. The process of claim 3 wherein the olefin is propylene. 